Metal Atoms Participate in the Self-Assembly and On-Surface Reaction Behaviors of 1,4-DBN on Ag(111) Surface

Herein, using 1,4-dibromonaphthalene (1,4-DBN) as the precursor molecule and Ag(111) surface as the substrate, we have characterized the various coordination and covalent structures formed by 1,4-DBN by low-temperature scanning tunnelling microscopy. We observed that there are three ordered structures (phase I, II, III) and one metal-organic short-chain structure (phase IV) at high coverage, meanwhile a new type of chiral structure (phase V) is observed coexisting with phase II, III, IV at low coverage. Surprisingly, all these structures have surface Ag adatoms incorporated. In addition, the phase III should be formed by a dissymmetric dehalogenation reaction of 1,4-DBN. Furthermore, we showed that the Ullmann coupling and cyclodehydrogenation of 1,4-DBN to form the armchair-shaped graphene nanoribbons will occur after thermal annealing. Combining the experiment data and density functional theory simulations, our results show that the surface Ag adatoms play a critical role in both the self-assembly and the on-surface reaction.

Automated summary

Using low-temperature scanning tunnelling microscopy, we investigated the coordination and covalent structures formed by 1,4-dibromonaphthalene (1,4-DBN) on Ag(111) surface. We found three ordered structures (phase I, II, III) and one metal-organic short-chain structure (phase IV) at high coverage, as well as a new type of chiral structure (phase V) coexisting with phase II, III, IV at low coverage. Notably, all these structures incorporate surface Ag adatoms. Furthermore, we demonstrated that thermal annealing can induce Ullmann coupling and cyclodehydrogenation of 1,4-DBN to form armchair-shaped graphene nanoribbons. Our results highlight the critical role of surface Ag adatoms in self-assembly and on-surface reactions.